The increasing demand for large power ratings and power density of power converters has been a key motivation for the research and development of new power semiconductors technologies. Power semiconductors have for decades been a topic of intensive research and continual improvement, and are used in applications such as hybrid vehicles, renewable energies, and industrial. Improving semiconductor efficiency and increasing power density are the main development topics. However, as the power density increases, the operating temperature of the device rises and causes thermal cycling issues and shortens the lifetime of the semiconductor.
To mitigate these problems, components called “reverse conducting” IGBTs (RC-IGBTs) have been developed. These semiconductors provide high power density and advantages in thermal cycling. They integrate an IGBT and an anti-parallel diode into a single chip and can operate as an IGBT (forward conduction mode) or as a diode (reverse conduction mode), which enables the discharging of the emitter during device turn-off [1]. As a result, the reverse recovery current peak can be reduced which leads to the reduction of switching losses.
As the RC-IGBT operates as an IGBT, it is known to apply standard switching pulses to the gate of RC-IGBTs, as with PWM or space vector modulation techniques for IGBTs. Further, it is also known to eliminate the modulation signals when the RC-IGBT is in reverse conduction mode [2][3][4]. The state, that is, either forward or reverse conducting of the RC-IGBT can be detected based on measurement of the collector-emitter voltage [3] [4] or measurement of the gate current of the RC-IGBT [2].
For reducing the switching losses it is suggested to apply a desaturation pulse to the gate of the RC-IGBT when the RC-IGBT is in reverse conduction mode [5]. The desaturation pulse in [5] is applied and ended before the gate pulse of a complementary switch component of a half-bridge connection receives its gating pulse. FIG. 1 shows a desaturation pulse presented in [5] in a half-bridge circuit. FIG. 1 shows a situation in which load current is positive and RC-IGBT T1 is in the diode mode. When T1 is in diode mode, the desaturation pulse is applied to the gate of T1 before a turn-on gate Uctrl,T2 signal is given to the switch component T2. Although the switching losses are reduced, the losses are not minimized when RC-IGBT is controlled in the above described manner.